全文获取类型
收费全文 | 790篇 |
免费 | 2篇 |
国内免费 | 2篇 |
专业分类
化学 | 611篇 |
晶体学 | 4篇 |
力学 | 16篇 |
数学 | 94篇 |
物理学 | 69篇 |
出版年
2023年 | 3篇 |
2022年 | 13篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 30篇 |
2012年 | 49篇 |
2011年 | 67篇 |
2010年 | 39篇 |
2009年 | 27篇 |
2008年 | 70篇 |
2007年 | 58篇 |
2006年 | 57篇 |
2005年 | 56篇 |
2004年 | 41篇 |
2003年 | 42篇 |
2002年 | 22篇 |
2001年 | 7篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 9篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有794条查询结果,搜索用时 0 毫秒
61.
Agnès Rivaton Sylvain Chambon Jean-Luc Gardette Stéphane Guillerez 《Polymer Degradation and Stability》2010,95(3):278-2251
Polymer-based organic solar cells are known to offer a poor stability in real use conditions, and the photodegradation of the active organic layer plays an important role in the reduced lifetime of the devices. This paper focuses on the photodegradation of two conjugated polymers used in organic solar cells, namely poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene (MDMO-PPV) and poly(3-hexyylthiophene) (P3HT), and their blends with [60]PCBM (methano-fullerene[6,6]-phenyl C61-butyric acid methyl ester), a fullerene derivative. MDMO-PPV and P3HT thin films were submitted to photoageing (λ > 300 nm) in the presence and in the absence of oxygen. The mechanisms by which these polymers degrade were elucidated. P3HT, pristine and blended with PCBM, was shown to be much more stable under illumination than MDMO-PPV. The results showed that, if deposited on an inert substrate and well protected from oxygen with a convenient encapsulation, P3HT:PCBM based active layer should be intrinsically stable for several years in use conditions. 相似文献
62.
Rached Salhi Ramzi Maalej Yannick Guyot Laetitia Rapenne Jean-Luc Deschanvres 《Journal of luminescence》2011,131(11):2311-2316
Erbium-doped Y2O3 films were prepared by aerosol-UV assisted metal-organic chemical vapour deposition (MOCVD) at 410 °C. The effects of humidity of carrier gas and UV-assistance on their structure and optical properties were investigated on the as-deposited and thermal annealed films using infrared spectroscopy, X-ray diffraction and transmission electron microscopy. It was found that the as-deposited Er:Y2O3 films crystallise in the Y2O3 cubic structure and present a very low organic contamination when the deposition takes place under high air humidity and, even better, with UV-assistance. After annealing, two different structural phases are observed corresponding to the cubic and the monoclinic structures of Y2O3. The Er3+ luminescence analysed in the visible and IR regions, shows the classical green transitions. The best optical properties were obtained with as-deposited and annealed Er:Y2O3 films grown under high air humidity with UV-assistance. Under such deposition conditions, 4I13/2 lifetimes was found to be 3.07 and 6.1 ms for films annealed at 800 and 1000 °C, respectively, and up-conversion phenomena were underlined. This indicates that the deposition conditions, in particular air humidity, play an important role in the luminescent properties even after annealing. 相似文献
63.
In inflationary models, the predicted amplitude of primordial density perturbations Q is much larger than the observed value (~10(-5)) for natural choices of parameters. To explain the requisite exponential fine-tuning, anthropic selection is often invoked, especially in cases where microphysics is expected to produce a complex energy landscape. By contrast, we find examples of ekpyrotic models based on heterotic M theory for which dynamical selection naturally favors the observed value of Q. 相似文献
64.
Estruch T Jaeck J Pardo F Derelle S Primot J Pelouard JL Haidar R 《Optics letters》2011,36(16):3160-3162
We investigate the strong electromagnetic coupling that settles in dual metallic grating structures. This coupling is evidenced to lead to a perfect optical extinction in the transmission spectrum. The behavior of this perfect extinction that strongly depends on the longitudinal space and the lateral displacement between the two gratings can be explained by a simple model that describes the interference between a propagating mode and a couple of evanescent modes. The results show that the electromagnetic transmission of the structure can be tuned by controlling the position of this perfect transmission extinction and thus pave the way to new types of infrared tunable filters. 相似文献
65.
Hitomi Anzai Makoto Ohta Jean-Luc Falcone Bastien Chopard 《Journal of computational science》2012,3(1-2):1-7
A modern technique to treat cerebral aneurysms is to insert a flow diverter in the parent artery. In order to produce an optimal design of such devices, we consider a methodology combining simulated annealing optimization and lattice Boltzmann simulations. Our results surpass, in terms of stent efficiency, those obtained in the recent literature with an other optimization method. Although our approach is still in 2D, it demonstrates the potential of the method. We give some hint on how the 3D cases can be investigated. 相似文献
66.
Jean-Luc Marichal Pierre Mathonet 《Journal of Mathematical Analysis and Applications》2011,380(1):105-116
By considering a least squares approximation of a given square integrable function f:n[0,1]→R by a multilinear polynomial of a specified degree, we define an index which measures the overall interaction among variables of f. This definition extends the concept of Banzhaf interaction index introduced in cooperative game theory. Our approach is partly inspired from multilinear regression analysis, where interactions among the independent variables are taken into consideration. We show that this interaction index has appealing properties which naturally generalize several properties of the Banzhaf interaction index. In particular, we interpret this index as an expected value of the difference quotients of f or, under certain natural conditions on f, as an expected value of the derivatives of f. Finally, we discuss a few applications of the interaction index in aggregation function theory. 相似文献
67.
Jean-Luc Guermond 《Numerische Mathematik》1994,67(4):465-473
Summary. L'objet de cet article
est de montrer que les estimations de
convergence sur la pression pour les m\'ethodes de
projection d\'ecrites
dans \cite{Shen1} et \cite{Shen2} ne sont pas obtenues correctement
car elles sont toutes bas\'ees sur une in\'egalit\'e fausse.
Il semble qu'on ait besoin d'une convergence en
de la vitesse
dans pour d\'emontrer les estimations
de convergence sur la pression en .
La question de savoir si la m\'ethode de projection a un taux
de convergence pour la pression plus \'elev\'e que
reste ouverte.
Received June 1, 1993 相似文献
68.
Jean-Luc Chabert 《Rendiconti del Circolo Matematico di Palermo》1994,43(1):51-70
We show that the sufficient conditions given by Cahen, Grazzini and Haouat for a version of the Stone-Weierstrass theorem in commutative algebra are the widest. More precisely, letA be a Noetherian ring andI a proper ideal ofA such thatA is Hausdorff with respect to theI-adic topology. Note the completion ofA andC(Â,Â) the ring of continuous functions from to with uniform convergence topology. The subset of polynomial functions is dense inC(Â,Â) if and only if the radical ofI is a maximal idealm ofA and the local ringA m is a one-dimensional analytically irreducible domain with finite residue field. 相似文献
69.
70.
Petra Hackenberg Jean-Luc Rioual Owen R. Tutty Philip A. Nelson 《Applied Scientific Research》1995,54(4):293-311
In recent years there has been an increasing interest in the control of boundary-layer transition through the use of wall suction. In the current work suction is provided through one or more suction panels situated close to the leading edge of a plate. Experiments show that boundary-layer pressure fluctuation measurements can be used to identify the position of transition. Transition can be maintained at a desired location with minimum power consumption by employing an automatic adaptive feedback control loop which regulates the suction flow rates of two independent suction panels. This can be expressed as a constrained optimization problem. To allow the suction flow rates to be updated, a modified least mean squares algorithm is used within the control loop. Experimental measurements show that the control algorithm allows fast and stable convergence towards the optimum suction distribution for a double suction panel configuration. Numerical simulations have also been performed. The two-dimensional boundary layer was calculated allowing the viscous boundary layer to interact with the inviscid outer flow. Following linear stability theory the spatial growth rates are calculated by solving an Orr-Sommerfeld type eigenvalue problem, with the streamwise location of transition predicted via thee
N -method. Applying the same optimization strategy as in the experiments, good qualitative agreement between computations and experiments was found. The optimization algorithm has been applied to computer models where the relation between suction flow rates and transition location is described by an empirical analytical function. This shows that the controller can in principle be applied to systems with more than two suction panels.Nomenclature
b
transition location with zero suction
-
d
desired transition location
-
e(k)
error signal
-
k
iteration index
-
p
rms pressure
-
p
ref
reference rms pressure
-
r
sum of the reference pressure
-
u
streamwise velocity
-
u
e
external velocity
-
inviscid external velocity
-
A
wave amplitude
-
F(
)
cost function
- I
identity matrix
-
N
maximum amplification factor
- P
projection matrix
- R
Reynolds number
- Re
Reynolds number based on the boundary-layer thickness
- R
matrix of weights
- Tu
turbulence level
-
vector of suction flow rates
-
v
normal velocity
-
v
wall
suction velocity at the surface
-
x
streamwise coordinates
-
x
m
microphone location
-
x
T(k)
measured transition location
-
y
normal coordinate
-
y(k)
sum of the measured pressures
-
w(k)
noise
-
plate length
-
r +i
i
-
free stream velocity
-
*
displacement thickness
-
gradient vector
-
Lagrange multiplier
-
controller gain
-
disturbance stream function
-
disturbance amplitude
-
wave frequency
= complex wave number 相似文献